Occurrence of subclinical post-streptococcal glomerulonephritis in family contacts.

Objective: There are few data in the published literature on the occurrence of subclinical post-streptococcal glomerulonephritis. In order to estimate the incidence of subclinical disease, 75 families of index cases with sporadic clinical post-streptococcal glomerulonephritis were screened for the presence of subclinical disease.
Methods: Three hundred and seventeen family contacts were investigated 1-7 days after the admission of the index cases. The diagnosis of subclinical disease was based on the presence of abnormal urinalysis, transitory hypocomplementaemia and increased antistreptolysin O titre.
Results: No cases of clinical/subclinical disease were detected among 147 parents. Abnormal urinalyses were found in 22.3% of sibling contacts. The incidence of nephritis among 170 siblings was 9.4% and the calculated ratio subclinical/clinical disease was 0.11. There were 16 siblings (9.4%) whose abnormal urinalyses could not be explained by appropriate tests; 11 of them had dysmorphic microhaematuria and significantly elevated antistreptolysin O titre.
Conclusions: Sibling contacts have increased risk for the development of clinical/subclinical post-streptococcal glomerulonephritis compared with their parents. Sibling contacts with unexplained urinary abnormalities might have subclinical nephritis in evolution; their complement levels normalized before occurrence of nephritis in index cases.